The present invention relates to a method of forming tubular wrappings on a cigarette packing machine.
More specifically, the invention relates to a method of continuously forming tubular wrappings on a cigarette packing machine, whereby groups of cigarettes are fed successively, at an input station, to a wrapping wheel rotating at constant angular speed about a respective axis.
In known methods, the wrapping wheel comprises a number of conveying heads, each of which oscillates about a respective axis parallel to the axis of rotation of the wrapping wheel, and receives, at the input station, a respective group positioned with its longitudinal axis parallel to said axis of rotation. When received by the respective conveying head, each group is already wrapped partly in a sheet of wrapping material, normally foil, folded into a U about the group of cigarettes and having, with respect to the group, two longitudinal end tabs projecting from the rear of the respective group in the traveling direction of the respective conveying head. Each head feeds the respective group to an output station, and, between the input and output stations, causes the respective group to cooperate with an external folding device, which normally comprises a number of outer folding members, normally fewer than the conveying heads, and which are fed by a conveyor along an annular path, and each oscillate with respect to the conveyor about a respective axis parallel to the axis of rotation of the wrapping wheel. Each outer folding member provides for squarely folding one of the tabs of a respective sheet of wrapping material, while the other tab of the sheet of wrapping material is normally folded by a further folding member fitted to the respective conveying head, to obtain a tubular wrapping.
In actual use, the outer folding member follows the respective group to contact one of the tabs, normally the one furthest from the axis of rotation of the wrapping wheel, and then rotates with respect to the relative conveyor to fold the tab.
The above known methods have several drawbacks, due to each outer folding member having to oscillate in controlled manner with respect to the conveyor to fold a respective tab. This poses not only construction problems, on account of the highly complex design of the external folding device, but also functional problems, in that any jamming of the tab with respect to, and during rotation of, the outer folding member may result in the tab being folded about the wrong fold line.
Moreover, each outer folding member necessarily cooperates with a number of conveying heads on the wrapping wheel, which therefore calls for painstaking setup of the conveying heads themselves.
It is an object of the present invention to provide a method of forming tubular wrappings, designed to eliminate the aforementioned drawbacks.
According to the present invention, there is provided a method of forming tubular wrappings on a cigarette packing machine; each tubular wrapping being formed from a sheet of wrapping material folded into a U about a respective group of cigarettes and having two end portions projecting from the rear of the group and defining a first and a second tab; the method comprising the steps of feeding each group continuously, by means of a respective substantially radial conveying head, along an annular path extending about a first axis, said second tab being interposed between said first tab and said first axis; and folding the two tabs of each said sheet of wrapping material onto the respective said group, as the group is fed along said annular path, to form a tubular wrapping about the respective said group; the method being characterized in that each said first tab is folded by means of a respective outer folding member, which is associated with the respective said conveying head, is located outwards of said annular path, and is movable to cooperate with the respective said first tab at a folding station; said outer folding members being equal in number to said conveying heads located along said annular path; and each said outer folding member being moved continuously and in such a manner as to remain substantially parallel at all times to the respective said conveying head.
The invention also relates to a unit for forming tubular wrappings on a cigarette packing machine.
According to the present invention, there is provided a unit for forming tubular wrappings on a cigarette packing machine; each tubular wrapping being formed from a sheet of wrapping material folded into a U about a respective group of cigarettes and having two end portions projecting from the rear of the group and defining a first and a second tab; the unit comprising a conveying drum rotating about a first axis; first actuating means for rotating said conveying drum continuously about said first axis; a number of conveying heads, each connected to said conveying drum in a respective substantially radial position, and each for receiving a respective said group with the respective sheet of wrapping material folded into a U, and with said second tab interposed between said first tab and said first axis; first and second folding means for respectively folding said first and said second tab of each said sheet of wrapping material onto the respective said group to form a tubular wrapping about the respective said group; and the unit being characterized in that said first folding means comprise, for each said conveying head, an outer folding member located outside said conveying drum and movable to cooperate with the respective said first tab at a folding station; said outer folding members being equal in number to said conveying heads; and second actuating means being provided to move each said outer folding member in such a manner as to keep the outer folding member substantially parallel at all times to the respective said conveying head.